1. Field of the Invention
The present invention relates generally to utility transmission and distribution, and in particular to a plastic crossarm for utility poles.
2. Description of the Prior Art
Utility poles are in widespread use for suspending utility lines, including electrical power, telephone, etc. at safe distances above a ground surface. Utility pole components have traditionally been manufactured predominantly of wood, which has the advantages of being relatively ubiquitous, in expensive, nonconductive, and generally at least adequate as a structural material with desired strength characteristics.
Disadvantages of wood include its susceptibility to damage from insects, birds, termites, etc. Wood is also subject to attack by biological organisms, particularly in humid environments. Still further, wood tends to deteriorate when exposed to the elements, such as ultraviolet radiation, precipitation, humidity, temperature cycles, etc. These and other factors have the cumulative effect of reducing the useful lives of structural members which are exposed to the elements and accessible to tests.
Plastic is often used as a replacement material for wood. For example, recycled plastic/composite railroad ties have been substituted for wood railroad ties. Still further, to maximize the useful life of exposed wooden structural members, standard practice is to coat them with a preservative, such as creosote. However, environmental laws and regulations significantly limit the permitted uses of wood preservatives, particularly those that contain toxins.
Although plastic materials tend to repel or resist water and are nonconductive, their disadvantages include susceptibility to ultraviolet radiation, higher densities as compared to wood and cost. The present invention addresses some or all of the disadvantages and limitations associated with wooden and plastic utility pole crossarm and crossarm assemblies. Heretofore there has not been available a utility pole crossarm, crossarm assembly, or manufacturing method with the advantages and features of the present invention.
In the practice of the present invention, a utility pole crossarm is manufactured from a plastic material and has a relatively dense outer surface and a less dense core. A crossarm assembly includes a plastic crossarm and a pair of diagonal braces for supporting the crossarm on the utility pole. A method of manufacturing the crossarm and the crossarm assembly includes extruding a continuous band comprising a polypropylene base material, a fiber reinforced plastic fill material, and a blowing or foaming agent. The materials are combined and extruded to form the continuous band, which is shaped and cooled in several stages and cut to predetermined lengths to form the crossarms.
Objects and Advantages of the Invention The principal objects and advantages of the present invention include: dividing a plastic crossarm for utility poles; providing such a crossarm which is resistant to the elements; providing such a crossarm which is resistant to pest damage; providing such a crossarm which meets or exceeds the strength specifications for wooden crossarms; providing such a crossarm which weighs approximately the same amount as a comparable wood crossarm; can be cut, drilled, etc. with tools used for working on wooden crossarm; providing such a crossarm which utilizes recycled plastic; providing such a crossarm assembly with a plastic crossarm and plastic braces; and providing such a crossarm which is economical to manufacture, efficient in operation, capable of a long operating life and particularly well adapted for the proposed usage thereof; providing a crossarm assembly with a plastic crossarm and plastic diagonal braces; and providing a method of manufacturing a plastic crossarm assembly.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.
The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.